1. Field of the Invention
This invention relates generally to automotive power steering systems and, more particularly, to variable effort power steering systems.
2. Description of the Prior Art
In typical power steering gears for automobiles, a valve which controls pressurization of the steering assist fluid motor is actuated by relative angular displacement between a spool rotatable with an input member of the steering gear and a sleeve rotatable with an output member of the steering gear. A torsion bar between the input and output members centers the sleeve and spool and resists such relative angular displacement between the input and output members. To increase "road feel" at highway speeds, detent type variable effort systems have been proposed wherein detents on the output member are urged by a fluid detent pressure into grooves in the input member. The detent pressure is produced by an auxiliary pump system including an auxiliary pump driven at speeds proportional to the speed of the vehicle. Since the detent pressure is effected by the viscosity of the detent fluid, unstable detent pressures may be experienced after cold starts. An auxiliary pump system according to this invention embodies a simple, economical and effective arrangement for minimizing the time duration after a cold start during which the detent fluid is susceptible to viscosity related pressure instability.